1. Technical Field
This invention relates to the art of making castings using a consumable pattern, commonly called the evaporative casting process (ECP), employing unbonded sand as the molding medium. This invention also relates, more particularly, to the technology for removing the solidified gating system attached to the metal casting.
2. Description of the Prior Art
ECP has become one of the major commerical innovations introduced recently by the foundry industry. It employs a consumable pattern made, typically, of polystyrene foam material in substantially the exact shape of the casting to be produced plus the shape of the sprue and runners forming the gating system within the mold for such casting. One of the great attributes of this process is the ability to embed the pattern in dry, unbonded sand (which may be fluidized by air followed by vibration to lock the sand grains in place about the pattern). There is no concern for a mold parting line or a pattern draft. The pattern material is ignited by poured molten metal, oxidized, and replaced by solid metal. The vaporized products of the pattern migrate outwardly through the interstices of the dry, unbonded sand.
Use of dry, unbonded sand allows the pattern design to be more complex and permits clustering of several castings about a common sprue (see U.S. Pat. Nos. 3,374,824 and 3,868,986 depicting simple, elementary, early versions of this concept). Clustering encourages closer positioning of the casting replicas relative to the central sprue to reduce temperature losses and metal return. In a large design, such as for an automobile manifold, the resulting cluster of castings will look like a tree with intricate branches projecting radially outwardly therefrom, creating a complex labyrinth of metal arms. The arms are usually the several runners leading to ingates at several locations along the casting replica.
The earliest mode used to separate the castings from the mold medium was to simply dump the entire contents of a mold flash onto a screen, the sand passing through the screen from the cluster of castings. The casting cluster was degated by cutting through the gating system labyrinth with a torch. In complex clusters, there is little access to a desired severance location, so time-consuming preliminary torch cuts must be made first. When access is provided, the final torch cuts are made at the juncture of the runner and usable casting. Because the complexity of the gating system prevents access of the torch to the innermost locations that must be severed, the cost of degating is increased and automation of such procedure is inhibited.
Accordingly, a primary object of this invention is to modify the solidification process of ECP so that much of the gating is easily disintegrated, allowing the casting to be removed as distinct, severed units. This would enable close, accurate, and robotic torch cutting of any residual gating; in the alternative, achieving disintegration would also allow simple impact severance of the residual gating without the need for torch cutting.